IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specification for implementing wireless local area network (WLAN) communication in the Wi-Fi (2.4, 3.6, 5, and 60 GHz) frequency bands. The 802.11 family consists of a series of half-duplex over-the-air modulation techniques that use the same basic protocol. The standards and amendments provide the basis for wireless network products using the Wi-Fi frequency bands. For example, IEEE 802.11ac is a wireless networking standard in the IEEE 802.11 family providing high-throughput WLANs on the 5 GHz band. Significant wider channel bandwidths (20 MHz, 40 MHz, 80 MHz, and 160 MHz) were proposed in the IEEE 802.11ac standard. The High Efficiency WLAN study group (HEW SG) is a study group within IEEE 802.11 working group that will consider the improvement of spectrum efficiency to enhance the system throughput in high-density scenarios of wireless devices. Because of HEW SG, TGax (an IEEE task group) was formed and tasked to work on IEEE 802.11ax standard that will become a successor to IEEE 802.11ac. Recently, WLAN has seen exponential growth across organizations in many industries.
In IEEE 802.11ac WLAN systems, a transmitter of a BSS (basis service set) of certain bandwidth is allowed to transmit radio signals onto the shared wireless medium depending on clear channel assessment (CCA) sensing and a deferral or backoff procedure for channel access contention. An enhanced distributed channel access protocol (EDCA) is used in IEEE 802.11ac as a channel contention procedure for wireless devices to gain access to the shared wireless medium, e.g., to obtain a transmitting opportunity (TXOP) for transmitting radio signals onto the shared wireless medium. The basic assumption of EDCA is that a packet collision can occur if a device transmits signal under the channel busy condition when the received signal level is higher than CCA level. This simple CSMA/CA with random back-off contention scheme and low cost ad hoc deployment in unlicensed spectrum have contributed rapid adoption of IEEE 802.11ac Wi-Fi systems.
Today, Wi-Fi devices are over-populated. Dense deployment has led to significant issues such as interference, congestion, and low throughput. Raising CCA levels has been shown to increase spatial reuse, which leads to significant increase in the network throughput in some dense deployment scenarios. In general, increasing CCA levels for inter-BSS packets can enhance the spatial reuse because more simultaneous transmissions can happen in multiple overlapping BSSs (OBSSs). However, raising CCA levels for spatial reuse also introduces more collision into the networks.
In IEEE 802.11ax WLAN systems, to enhance spatial reuse and avoid collisions, a BSS color is inserted into the signal field for each HE packet. When a station (STA) receives a HE packet, by resolving the BSS color, the STA might be able to identify that the packet is from OBSS (called inter-BSS) or from its own BSS (called intra-BSS). When spatial reuse is applied, channel contention schemes should be different for inter-BSS and intra-BSS packets. In a dense WLAN environment, however, BSS color is not always resolvable for a given STA because the received packet can be the superposition of multiple packets. A solution is sought to enhance the channel contention scheme such that spatial reuse can be enabled when BSS color cannot be resolved.